This invention relates to the field of CMOS devices. More particularly, this invention relates a dual gate oxide CMOS device.
This invention is useful in, for example, power amplifiers for cellular telephone systems, and other wireless transmission systems.
Some prior art RF power amplifiers use two active switching devices to generate a square wave signal. An output load network filters and transforms the signal into a sinusoidal output signal which is then transmitted. There are various problems associated with this type of power amplifier. Perhaps the largest problem with power amplifiers involves the efficiency of the amplifiers. When RF power amplifiers are used to produce high power signals, such as with transmitters, it is desired to have efficient amplifiers in order to conserve power and adequately dissipate heat. This problem is especially hard to overcome in designs utilizing CMOS devices.
Another problem relates to the use of an isolation transformer. Some prior art RF power amplifiers include a transformer connected between the pre-driver circuitry and the amplifier circuit. This presents various issues. First, a transformer is required, which uses valuable real estate on a printed circuit board (PCB) and also increases the cost of the amplifier. In addition, the transformer consumes power and generates heat.
Another problem with prior art power amplifiers involves voltage regulators. During battery charge up, the battery voltage can be much higher than the steady-state voltage. Applying this high voltage directly to a CMOS power amplifier can cause breakdown problems. Therefore, a voltage regulator may be required to provide a regulated voltage source. However, when the battery charge is high and the power amplifier is transmitting at maximum power, there is a high power dissipation in the voltage regulator which could exceed the package power rating of an integrated circuit.
When selecting the types of devices to be used in a CMOS design, such as an RF power amplifier, certain tradeoffs exist. For example, devices with smaller gate oxide thickness are faster and take up less space. However, as the gate oxide thickness gets smaller, the breakdown voltage of the device also gets smaller. Therefore, when selecting devices in a CMOS design a problem develops in getting a suitable breakdown voltage as well as a suitable speed for a device.
Another problem with prior art power amplifiers relates to amplifiers using a push-pull architecture. A push-pull architecture requires very low inductance and resistance in the ground and signal connections of the integrated circuit to the PCB. In a typical wire bond package, the bond wire inductance can be large enough to cause problems. In addition, the resistance of on-chip wiring using thin on-chip conductors can cause significant losses.
A dual gate oxide CMOS device of the present invention includes first circuitry having one or more components having a first gate oxide thickness, and second circuitry having one or more components having a second gate oxide thickness, wherein the first and second gate oxide thicknesses are different.
Another embodiment of a dual gate oxide CMOS power amplifier includes an input stage having pre-driver circuitry comprised of devices with a first gate oxide thickness, and an output stage having amplifier circuitry comprised of devices with a second gate oxide thickness, wherein the first gate oxide thickness is less than the second gate oxide thickness.
Another embodiment of the present invention provides a method of providing a power amplifier including the steps of providing circuitry having a plurality of components, forming a first portion of the plurality of components using devices having a first gate oxide thickness, and forming a second portion of the plurality of components using devices having a second gate oxide thickness, wherein the second gate oxide thickness is greater than the first gate oxide thickness.
Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.